Recent advances in microsensor design can be used to refine the technology of intramuscular pressure measurement. The overall objective of this project is to design, develop, and test a fiber optic microsensor which can be used for routine, clinical measurement of muscle function. Currently, the integrated electromyogram is used to indicate the timing and intensity of muscle contraction. However, the problem remains that electromyographic activity cannot provide a quantitative measurement of muscle tension under dynamic conditions. An alternative, measurable parameter related to muscle force is intramuscular pressure. It is thought that intramuscular pressure will account for both active and passive muscle tension. However, currently available intramuscular pressure transducers are too large for optimum comfort. Microsensor technology is now available to construct transducers which are approximately the same size as the fine wires used for electromyographic analysis. The specific aims of this study are to (1) design and construct a fiber optic microsensor for measuring intramuscular pressure, and (2) determine the relationships between intramuscular pressure, muscle sarcomere length, and muscle tension in an animal model. Successful development of this microsensor will result in a powerful new tool for quantifying muscle function. This device will be useful in offering a better representation of muscle tension under dynamic conditions. It will become an essential tool in clinical gait analysis aimed at improving mobility of disabled patients with neuromuscular disorders such as cerebral palsy, stroke, head injury, spinal cord injury, and poliomyelitis.